hey guys i just orderd some new wheels and i noticed when i opened up the box that my tire sizes were differant....they sent me 245/40zr18 for the fronts and for my rears they sent me a smaller 275/35zr18...now i'm not talking about the wideness of the wheel but the overall diameters are differant.Shouldn't they have sent me 245/40 and 275/40 instead of 40 and 35 for my rears?Did they do this on purpose?Is this normal? if so why?


Sorry for the ignorant questions but i'm a bonehead when it comes to tires and wheels...i wasent even aware that my tires were differant sizes when i purchased them

 

it's fairly common to have either 40 or 35 series in the rear. it's just a matter of preference, but this is probably why they sent it w/ 35s

if you have 275/35 on the rear, your overall tire diameter will be closer to that of the front wheels.
the aspect ratio is 35% of 275mm. or a sidewall height of 96.25mm.
for 40 series it's 110mm.
The fronts being 245/40 = 98mm.

most people want their cars to sit flat and having 35s in the rear will help do that. I however like to have a larger sidewall in the rear for tire flex/grip so that's why I have 40 series in the rear even thoughit gives my car a slight rake. The tire sizes also slightly affect acceleration, but not a lot.

 

This is not normal and it is a badddd setup. The Z is designed with a stagger which means the front tire is supposed to be smaller than the rear. In this case you have the complete opposite. Plus its gona look funky on the car when your rear tires have a smaller sidewall than the front.

This is almost def a mistake, unless you wanted it this way. The sidwall height should be the same for the front and the rear, but having the rear smaller is terrible.

It will effect a bunch of stuff including handeling, traction, traction control or vds, etc.

This is a big no no!

 

Did you not know what the sizes were when you bought the wheels?

 

well not i must have overlooked it...i guess i just kind of paid attention to the 245 and 275 sizes that when he was telling me the sizes it just kind of went by me to be honest...as stupid as that might sound....or he initially told me the right sizes but there was a mistake when he shipped them ...not sure....



But one thing i did notice if you guys check out this months road and track speed magazine they do a comparo between a few tuner Z's and most are all running the same set up i am which is 40's in the front and 35's in the rear so maybe this is a good thing?I mean if thats what the expert tuners were running on their cars(stillen,vortech,axis,and greddy...obviously they would know about the tire sizes and possible vdc issues i'm assuming

 

It won't look funky at all. Do some reasearch on tire sizing. The second number is a percentage of the first number. 35% of 275 is almost the same as 40% of 245. This is the optimum setup for 18"s.

http://www.miata.net/garage/tirecalcold.html

 

ok but your comparing the fronts which are supposed to be smaller to the rears which are supposed to be larger.

You want to keep the stagger! Ya 245/40 front and 275/35 rear will be the same size, but thats the problem. You dont want them to be the same. You want the rears to be larger.

I could be wrong ofcourse, but this is what ive gathered from looking at common setups.

 

first rule of fight club: never go with smaller sidewall in back.
i'd be pissed. it won't look right.
there is a range of stagger you want to adhere to. i forget what it is, but the info can be found on this site.